Substrates composed predominantly of cellulosic materials are frequently advantageously strengthened by treatment with a polymeric composition. The treatment with a polymeric composition may also provide reduced sensitivity to moisture vapor or water or solvents in addition to reinforcement of the substrate. Furthermore, the polymeric composition should not substantially detract from essential substrate characteristics, as might be the case, for example, if the cured composition were too rigid or brittle or became sticky under processing conditions. Additionally, the polymeric composition should wet out and penetrate preformed cellulosic webs and mats.
There is a need for a method for strengthening cellulosic substrates by treating with a curable aqueous composition which is free from formaldehyde, because of existing and proposed legislation directed to the lowering or elimination of formaldehyde.